Downloading and Updating Xcode and SDKs

The current release of Xcode is available as a free download from the Mac App Store. The Mac App Store will notify you when an update is available or you can have OS X update automatically as it becomes available.
The latest beta versions of Xcode can be downloaded from the Xcode download page. Previous versions of Xcode can also be downloaded here. To download beta or previous versions of Xcode, simply sign in with your Apple ID. Program membership is not required.

Providing Feedback and Reporting Bugs

Your feedback goes a long way towards making Xcode even better. With Apple Bug Reporter,
you can report issues or request enhancements to APIs and tools.
Include detailed information about issues, including the system and
developer tools version information, and any relevant crash logs or
console messages.To provide feedback or ask questions, post your
questions and comments on the Apple Developer Forums.

Submitting Apps to the App Store using Xcode

If you're an Apple Developer Program member, Xcode provides an integrated workflow to prepare and submit apps to App Store. You should use the latest version of Xcode available on the Mac App Store to submit your apps, or when available, the latest GM seed release from the Xcode download page. For more information, read the App Distribution Guide.
Do not submit apps built using beta software, as beta versions of
Xcode, Operating Systems, and SDKs are for development and testing only.

Invalid Private Key and Certificate Pairing

If you received an error message saying, "Xcode could not find a
valid private-key/certificate pair for this profile in your keychain."
This error message indicates that the Keychain Access application on your Mac is missing either the public or private key for the certificate you are using to sign your app.
This often happens when you are trying to sign and build your
app from a different Mac than the one you originally used to request
your code signing certificate. It can also happen if your certificate
has expired or has been revoked. Ensure that your app's provisioning
profile contains a valid code signing certificate, and that the Keychain Access application on your Mac contains that certificate, the private key originally used to generate that certificate, and the WWDR Intermediate Certificate.
For instructions on how to resolve this and other code signing erros, review the Code Signing Support page.

Learn More

The Apple developer website contains a wealth of documentation,
videos, and community-based information to help you develop with Apple
technologies using Xcode.

Apple Security Updates

from https://developer.apple.com/support/xcode/,https://developer.apple.com/xcode/https://developer.apple.com/xcode/ide/https://developer.apple.com/xcode/features/https://developer.apple.com/xcode/download/ -------------------

Innovative tools help you create great apps• Swift is a revolutionary programming language that is safe, fast, and modern• Playgrounds are a fun place to experiment with Swift code, displaying instant results• Interface Builder is a graphical UI design canvas with a live preview of your app• View debugging shows a 3D stack of all your app's UI view layers at runtime• Assistant editors show content related to your primary task• Live Issues display errors as you type, and Fix-its can correct mistakes for you

Swift is a powerful, modern, and fun programming language• Safe by design, Swift syntax and features prevent entire categories of bugs• Fast code execution and compile time are powered by the proven LLVM compiler• Modern language features are inspired by leading research, including:- Closures unified with function pointers- Tuples and multiple return values- Structs as value types that support methods, extensions, protocols- Powerful protocols that can extend functionality throughout your codebase- Functional programming patterns including map and filter

Interface Builder makes it easy to design your interface without code• Storyboards let you arrange the complete flow of screens within your app• See your custom controls rendered live within the design canvas• Preview your interface in different screen sizes, orientations, or languages• StackViews make it easy to reason about the layout of each section of your interface• Create connections from your GUI design directly to the related source code

Professional editor and debugger keep your code front and center• Hit a few keys and Open Quickly will instantly open any file within your project• Message bubbles show errors, warnings, and other issues right beside your code• Data tips show a variable's value by hovering your mouse over the code• Quick Look variables while debugging to see the actual color, bezier path, image, and more

Apple LLVM technology finds and fixes bugs for you• Analyzer travels countless code paths looking for logical errors before they become bugs• Live Issues identifies coding mistakes as you type with no need to build first• Fix-it can confidently correct mistakes for you with just a keystroke

Test driven development is built right in• Use the Test Navigator to add, edit, or run unit tests or user interface tests with just a click• Test Assistant makes it easy to edit your code and related tests, side-by-side• Create continuous integration bots using OS X Server to automatically build and test your apps• Monitor performance and user interface test data using OS X Server to immediately spot regressions

To
test or deploy applications on an iOS device, Apple TV, or on Apple
Watch all you need is a free Apple ID. To submit your apps to the App
Store you must be a member of the Apple Developer Program. Continuous
integration features require a current version of OS X Server. Some
features may require Internet access.from https://itunes.apple.com/us/app/xcode/id497799835?ls=1&mt=12 注：程序文件的大小为3.8gb.最好挂vpn后，才下载。否则很难下载成功。